These vowel combinations are (mostly) not short or long, but make completely different vowel sounds. (OI/OY & OU/OW are formed with mouth positions that change, the definition of diphthong. AU/AW & OO/OO may be called vowel digraphs – two letters that combine to make one sound)

Note that AU/AW is a diphthong that makes a Short O sound, and that OW can also make a Long O sound in some words (like know and blow). Exceptions: OU can say OR like in pour or OO like in soup. It also makes a different sound when followed by the letters ld or gh.